Electroactive biofilms: how microbial electron transfer enables bioelectrochemical applications

Abstract

Microbial biofilms are ubiquitous. In marine and freshwater ecosystems, microbe-mineral interactions sustain biogeochemical cycles, while biofilms found on plants and animals can range from pathogens to commensals. Moreover, biofouling and biocorrosion represent significant challenges to industry. Bioprocessing is an opportunity to take advantage of biofilms and harness their utility as a chassis for biocommodity production. Electrochemical bioreactors have numerous potential applications, including wastewater treatment and commodity production. The literature examining these applications has demonstrated that the cell-surface interface is vital to facilitating these processes. Therefore, it is necessary to understand the state of knowledge regarding biofilms' role in bioprocessing. This mini-review discusses bacterial biofilm formation, cell-surface redox interactions, and the role of microbial electron transfer in bioprocesses. It also highlights some current goals and challenges with respect to microbe-mediated bioprocessing and future perspectives.

Keywords: Bioelectrochemical systems; Biofilms; Extracellular electron transfer; Extracellular electron uptake; Microbial electrosynthesis.

Fig. 1

Relevant areas of consideration for optimizing electroactive biofilms in bioelectrochemical applications. Efficient design and operation of bioelectrochemical systems rest on fine-tuning bioelectrochemical cell parameters using tools such as mathematical modeling to allow for scalability; investigation of microbe–electrode interactions and the effect of electrode type, electrode modifications, microbial composition, and biofilm formation on performance; and understanding the cellular processes underlying electron exchange and product formation. Future efforts to improve bioelectrochemical cell performance should focus on improving Coulombic efficiency, optimizing biofilm formation, enhancing bioproduct formation, and bioprospecting for novel electroactive strains and electron exchange mechanisms.